Daniel Yergin, chairman of IHS Cambridge Energy Research Associates and a Pulitzer Prize-winning author, argues in a WSJ.com Saturday Essay that Peak Oil theory has a fatal flaw, which is rooted in Hubbert’s (the man who came up with the idea of peak oil) blind spot: economics

Actually, the biggest flaw is that it does not really account for the substitution effect. At some point, oil prices become high enough that it becomes economically viable to manufacture synthetic gas from coal and other sources. As prices rise, people will turn to other sources of energy reducing demand for oil. Peak oil proponents are not very keen observers of history. For example, I don't see a sperm whale lamp oil or peat shortage.